Comments made by affected user

We are using ServiceDesk 7.5 MP1. Is anyone aware of a method to have the owner of an incident notified by email if the affected user adds a comment to the ticket? I've tried looking at creating a rule based on OnCommentAdded but the only available options appear to be if the comment is made by a specific user (cant designate affect3ed user here) or the comment contains text/is specific value/starts with.Thanks